β-diversity decreases with increasing trophic rank in plant - arthropod food chains on lake islands

Contrasting trophic theories of island biogeography try to link spatial patterns in species distribution and richness with dietary preferences, arguing that the spatial turnover of species among habitat patches changes with trophic rank causing a systematic change in the proportion of plants, herbivores, and predators across habitats of different size. Here we test these predictions using quantitative surveys of plants, spiders, and herbivores as well as of omnivorous and predatory ground beetles on undisturbed Polish lake islands. We found decreased proportions of predators and habitat generalists on larger islands. Environmental niches and niche overlap were highest in predators. Variability in environmental niche width among species increased at higher trophic levels. Our results confirm models that predict a decrease in spatial species turnover (β-diversity) with increasing trophic level. We speculate that the major trigger for these differences is a reduced dispersal ability in plants at basal trophic ranks when compared to higher trophic levels.

Effects of increasing nutrient disturbances on phytoplankton community structure and biodiversity in two tropical seas

Statistical analysis of rainfall data from 2005 to 2015 showed that atmospheric deposition supplied large amount of dissolved inorganic nitrogen (38-155 mg·m^-2·month^-1) in N-deficient South China Sea and Eastern Indian Ocean. To understand marine ecosystem responses to increasing nutrient disturbances, we implemented field mesocosm experiments to study phytoplankton community structure and biodiversity responses to nutrient treatments with nitrate, phosphate and iron across tropical seas. Our results showed that DIN supply would change phytoplankton community structure and stimulated the regime shift from cyanobacteria to diatoms (relative dominance R > 0). Phytoplankton communities were dominated by diatoms (relative abundance >50%) accompanied by high chlorophyll a content with 1.58-39.27 μg·L^-1 in DIN-added cultures, whereas cyanobacteria dominated communities (relative abundance >60%) with low biomass of 0.12-0.18 μg·L^-1 in undisturbed cultures. Simultaneously increased DIN loading from atmospheric deposition would decrease ecological diversity of tropical seas owing to species competition and succession (Shannon diversity H' decreased to <1).

Anthropogenic modification disrupts species co-occurrence in stream invertebrates

The question of whether species co-occurrence is random or deterministic has received considerable attention, but little is known about how anthropogenic disturbance mediates the outcomes. By combining experiments, field surveys and analysis against null models, we tested the hypothesis that anthropogenic habitat modification disrupts species co-occurrence in stream invertebrates across spatial scales. Whereas communities in unmodified conditions were structured deterministically with significant species segregation, catchment-scale conversion to agriculture and sediment deposition at the patch- or micro-habitat scale apparently randomized species co-occurrences. This shift from non-random to random was mostly independent of species richness, abundance and spatial scale. Data on community-wide life-history traits (body size, dispersal ability and predatory habits) and beta-diversity indicated that anthropogenic modification disrupted community assembly by affecting biotic interactions and, to a lesser extent, altering habitat heterogeneity. These data illustrate that the balance between predictable and stochastic patterns in communities can reflect anthropogenic modifications that not only transcend scales but also change the relative forces that determine species coexistence. Research into the effects of habitat modification as a key to understanding global change should extend beyond species richness and composition to include species co-occurrence, species interactions and any functional consequences.